Conventionally, a microscope has been used to detect the number of pollen particles floating in air using a visual inspection process in which a glass plate is exposed to air for some time to collect pollen particles. The glass plate is stained, followed by a skilled technician's counting by visual inspection the stained particles through his or her microscope (hereinafter referred to as the “microscope method”).
The above microscope method is a lengthy time consuming process requiring advanced skills to count the stained pollen particles by visual inspection. In addition, the microscope method does not permit pollen particles to be detected on a real time basis which is a significant drawback. The place for taking measurements using a microscope is also very limited, which is another drawback.
It is also known to detect pollen particles on a real time basis utilizing polarized light. This alternate method is disclosed in Japanese Patent No. 3113720 and in Japanese Patent Publication No. 2001-83079. The pollen detector described in Japanese Patent No. 3113720 does not require the expertise that the microscope method requires, and the measurement result can be obtained anywhere on a real time basis. Nevertheless, the quantity of pollen particles floating in air is so small that to increase the available number of pollen particles, a large volume of air should be blown into the detection zone. However, this also increases the probability of other floating particles being simultaneously passed into the detection zone. Since the pollen detector described in Japanese Patent No. 3113720 cannot discriminate pollen particles from other floating particles, the pollen detector is prone to error. Moreover, either a decrease in luminous energy emitted from the light source over time or lens contamination will reduce the intensity of the scattered light beams, making it even more difficult to discriminate pollen particles from other particles.
A similar detection device is described in Japanese Patent Publication No. 2001-83079 which is capable of measuring floating particles in real time. This device cannot discriminate pollen particles from other particles passed through the detection zone when the volume of air blown into the detection zone is increased. Accordingly, this device has the same deficiencies as the pollen sensor described in Japanese Patent No. 3113720.